astronomy

NGC 7720

NGC 7720 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NGC 7720 rather than just read about it. In short: NGC 7720 is an elliptical galaxy located in the constellation Pegasus. It is located at a distance of about 380 million light years from Earth, which, given its apparent dimensions, means that NGC 7720 is about 180,000 light years across.

Key takeaways

NGC 7720 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 7720 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 7720 from memory before moving on to harder problems.

Reference excerpt

NGC 7720 is an elliptical galaxy located in the constellation Pegasus. It is located at a distance of about 380 million light years from Earth, which, given its apparent dimensions, means that NGC 7720 is about 180,000 light years across. NGC 7720 is the main galaxy of Abell 2634 galaxy cluster and is a radio galaxy. It was discovered by William Herschel on September 10, 1784.

Characteristics

NGC 7720 is made of a galaxy pair that is separated by 12 arcseconds. The south galaxy is the one associated with the radio source. In the centre of the galaxy lies a dust disk is visible nearly face on. The dust mass of NGC 7720 is estimated to be between 106 to 107 M☉. There is also ionized Hα+[N II] gas emission from the disk. NGC 7720A features too a dusty disk.

Radio jet

NGC 7720 is a Fanaroff-Riley type I radio galaxy, and is also categorised as a wide angle tail (WAT) radio galaxy. It has two asymmetrical radio jets that emerge from the bright radio core. The core didn't exhibit variability when observed by the Very Large Array (VLA). In parsec scales, the jet is one sided features relativistic motion, about 0.6 times the speed of light, and has a northwest direction. The northwest jet is the main one and forms a distorted plume about 5 arcminutes long, with a hotspot about 30 arcseconds from the core. The southeastern jet has a bright spot about 30 arcseconds from the core and then fans to a distorted plume that extends for 5 arcminutes. In large scales the jets appear bend, maybe due to ram pressure as the galaxy moves through the intracluster medium. X-ray emission has been detected by the radio jet, indicating the contribution of synchroton mechanism to the creation of the jet. The radio plumes are regions with decreased X-ray emission. The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 7720 is estimated to be 109.28 (1.9 billion) M☉ based on stellar velocity dispersion or 109.26 (1.81 billion) M☉ based on mass of the bulge.

Nearby galaxies NGC 7720 is the dominant galaxy in Abell 2634 galaxy cluster. It is classified as a poor galaxy cluster and has a total X-ray luminosity of (1.4±0.3)×1044 erg/s, which is considered low in relation to other similar clusters. X-ray bolometric luminosity has a central peak which corresponds to NGC 7720, while excess emission is to the southwest, perpendicularly to the radio jets. About 118 galaxies lie within half degree from the centre of the cluster and are considered to be members of the cluster. Abell 2634 forms a pair with galaxy cluster Abell 2666, which is located 3 degrees to the east, but has lower redshift. Both clusters lie behind the Perseus–Pisces Supercluster. Abell 2622 lies behind Abell 2634, at about double the redshift.

See also NGC 383 - a similar radio galaxy

References

External links

NGC 7720 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 7720 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 7720

Start with the simplest possible case. Write down what NGC 7720 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NGC 7720 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NGC 7720 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NGC 7720

In research: NGC 7720 appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NGC 7720 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NGC 7720 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3C objects, 4C objects, Astronomical objects discovered in 1784, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 7720 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study NGC 7720 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 7720 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NGC 7720 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 7720 in simple terms?

Why does NGC 7720 matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NGC 7720?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NGC 7720.